It is possible to record on various recording medium by the ink jet recording method.
In order to record better images, various inks, for example, an ink suitable for recording images with the image quality of a photograph on glossy paper or the like and an ink suitable for recording documents on plain paper or the like, in accordance with the purposes have been proposed. In recent years, the ink jet recording method has been utilized for printing a business document including characters and charts, where plain paper or the like is used as a recording medium. The frequency of utilization for such an application has increased significantly. In such an application, a further enhancement in color developability of an image is required. In addition, the recording speed is important and, therefore, an improvement in ejection characteristics of an ink is required than ever.
In response to the above-described requirements, there are proposals taking note of the types of functional groups which are bonded to self-dispersible pigments (refer to PTL 1 and PTL 2). PTL 1 describes an ink containing a self-dispersible pigment, in which a functional group, e.g., a carboxylic acid group, is bonded to a particle surface, and a salt, and it is stated that the color developability of an image is enhanced as the density of the functional group on the particle surface becomes high. PTL 2 describes an ink containing a self-dispersible pigment in which a functional group having high reactivity with calcium is bonded to the surface of a pigment particle. PTL 2 further describes an ink containing a self-dispersible pigment with a phosphonic acid group and a self-dispersible pigment with another functional group, and an ink containing a self-dispersible pigment with a functional group including both the phosphonic acid group and the carboxylic acid group.